It would probably be possible, but it would be pretty difficult. You would need to figure out how to make the proper geometry for the bike, which will take some planning. You should not need any type of internal sleeve, it should be completely unnecessary and will make the bike heavier. Doing so would also make it difficult to get a result that looks good and is structurally sound. If you have not worked with carbon fiber before, it can pretty difficult to work with.
If you want to do go ahead and do this I could offer some potentially useful advice, having just done something similar to this with a steel bike frame and also having worked with carbon fiber before.
This is one option for cuts you can make to the bike. You should note that this plan may cause some probably solvable issues, e.g. brake bridge in the wrong spot, since you are switching wheels size. Cut the bike apart, shorten the down tube and seat tube as necessary. You may need to shorten the head tube. For the next step you have a few options.
1) Reattach your head tube to the shortened down tube then put in the top tube by shortening it as necessary.
2) Try to put both the head tube and top tube in at the same time.
3) Make a second cut to the top tube and discard the carbon seat cluster. Use a piece of seat tube from an aluminum or steel frame for the top part of your seat tube.
Then you need to reattach the seat stays, which should be fairly easy. You will probably need to get creative when trying to figure out the rear brake bridge/boss and small parts such as cable stops.